There are many published reports concerning the ability of human milk to protect the suckling infant from gastrointestinal infection. See, A. S. Cunningham, Morbidity in breast-fed and artificially fed infants, J. Pediatr., 1979, Vol. 95, p. 685-689; M. G. Myers et al., Respiratory and gastrointestinal illnesses in breast- and formula-fed infants, Am. J. Dis. Child., 1984, Vol. 138, p. 629-632; S. A. Larsen, Jr., Relation of breast versus bottle feeding to hospitalization for gastroenteritis in a middle-class U.S. population, J. Pediatr., 1978, Vol. 92, p. 417-418; M. E. Fallot et al., Breast-feeding reduced incidence of hospital admissions for infection in infants, Pediatr., 1980, Vol. 65, p. 1121-1124; A. S. Cunningham, Breast-feeding and health, J. Pediatr., 1987, Vol. 110, p. 658-659. Much of this protection has been attributed to the presence of immunogobulins in the milk. See, G. A. Loslonsky et al., Maternal-neonatal interactions and human breast milk, In: Reproductive Immunology, N. Gleicher (ed.), New York, Alan R. Riss, 1981, p. 171-182; A. S. Goldman et al., Host defenses: development and maternal contributions, In: Barness LA., ed., Advance in pediatrics, Vol. 32, 1985, p. 71-100. However, it has also been shown that there are nonspecific factors in milk which can kill pathogens or slow their replication. Some of these protective factors are also nutrients, such as monoglycerides and fatty acids. Since human infant formula does not contain immunoglobulins, it has been assumed that it does not confer any protection against gastrointestinal infection. However, formulas do contain triglycerides which, following lipolysis in the stomach and intestine, produce free fatty acids and monoglycerides of which some have been shown to inactivate enveloped viruses and Giardia lamblia when present in human and bovine milk. See, J. K. Welsh et al., Use of Semliki Forest virus to identify lipid-mediated antiviral activity and anti-alphavirus immunoglobulin A in human milk, Infect. Immun., 1978, Vol. 19, p. 395-401 (I); J. K. Welsh et al., Effect of antiviral lipids, heat, and freezing on the activity of viruses in human milk, J. Infect. Dis., 1979, Vol. 140, p. 322-328 (II); C. E. Isaacs et al., Membrane disruptive effect of human milk: Inactivation of enveloped viruses, J. Infect. Dis., 1986, Vol. 154, p. 966-971, all of the aforementioned articles being incorporated herein by reference.
Human milk contains a number of antiviral factors that are not immunoglobulins. See, W. A. Falkler, Jr., et al., A lipid inhibitor of dengue virus in human colostrum and milk, Arch. Virol., 1975, Vol. 47, p. 3-10; A. H. Fieldsteel, Non-specific antiviral substances in human milk active against arbovirus and murine leukemia virus, Cancer Res., 1974, Vol. 34, p. 712-715; T. H. Matthews et al., Antiviral activity in milk of possible clinical importance, Lancet, 1976, Vol. ii, p. 1387-1389; N. H. Sarkar et al., Effect of human milk on the mouse mammary tumor virus, Cancer Res., 1973, Vol. 33, p. 626-629. Some of these factors are located in the nonlipid fraction of the milk, but most studies found antiviral activity associated with the lipid fraction. Antiviral lipids were best characterized by Welsh et al. (II), who found that free unsaturated fatty acids and monoglycerides in milk inactivated enveloped, but not nonenveloped, viruses.
As reported in C. E. Isaacs et al., Membrane Disruptive Effect of Human Milk: Inactivation of Enveloped Viruses, J. Infect. Dis., 1986, Vol. 154, p. 966-971, specifically incorporated herein by reference, the work of Welsh et al. (II) has been confirmed and extended. It was shown that lipids from fresh breast milk are not antiviral but become active against enveloped viruses upon storage at 4.degree. C. and in infant stomachs, probably by the release of fatty acids from milk triglycerides.